Segregation of altered parental properties in fusions between Saccharomyces cerevisiae and the D-xylose fermenting yeasts Candida shehatae and Pichia stipitis.

A prototrophic strain of Saccharomyces cerevisiae CSIR Y190 MATa xyl-, resistant to high levels of ethanol, was hybridized with xylose-fermenting, auxotrophic mutants of Candida shehatae and Pichia stipitis through polyethylene glycol-induced protoplast fusion in an attempt to produce ethanol-tolerant, xylose-fermenting hybrids. Mononucleate fusants were obtained, but these dissociated into a mixture of parental-type segregants. Purified Candida- and Pichia-resembling segregants failed to acquire improved ethanol tolerance but expressed other novel properties of S. cerevisiae, suggesting that karyogamy was impaired after internuclear gene transfer.